When a message fails delivery because of a 4xx series error code, the response is checked against a list of signatures. If a signature is matched, it is considered a greylisting and the retry time is
shortened to the value specified. Since response codes change and new ones are always popping up, you may need to add your own signatures. To do this you need to edit the optimizations.list file in the main config directory.
The file is formatted by using a single line for each entry. The line contains the string to search for in the server response, a pipe symbol |, and the number of minutes to defer. The minutes to defer
value must be shorter than the standard retry time.
Currently the file contains the below values.
deferred | 8
Greylisted | 8
Grey listed | 10